Formation of Vivianite in Excess Waste Activated Sludge and its Correlation with Fe(III) Reduction
2021; RELX Group (Netherlands); Linguagem: Inglês
10.2139/ssrn.3982901
ISSN1556-5068
AutoresThomas Prot, Wout Pannekoek, C. Belloni, Lulian Dugulan, Ruud Hendrikx, Leon Korving, Mark C.M. van Loosdrecht,
Tópico(s)Adsorption and biosorption for pollutant removal
ResumoThe iron phosphate mineral vivianite (Fe3(PO4)2⋅8H2O) received increasing attention since its ubiquity in digested sludge was shown in recent years. Vivianite can be magnetically extracted from digested activated sludge which opened a new route for phosphorus recovery. While its formation in digested sludge is regularly reported, it is not yet studied for fresh, undigested activated sludge. In particular, the extent to which vivianite could form during sludge storage is missing. The current research with full scale WAS confirmed that the iron reduction rate in thickened sludge followed first-order rate kinetics with reduction rate constants of 0.03-0.05 h-1. The reduction was completed after 2-4 days of anaerobic storage, and the vivianite appeared to form quickly from the pool of reduced iron made available. After sludge thickening at the WWTP (30 hours retention time), around 11% of the iron was vivianite. With subsequent 1-3 days of anaerobic storage, this fraction increased to 50-55%. After this storage, almost all the vivianite that could potentially form did form. The remaining iron was present as FeSx, which preferentially formed over vivianite and soluble iron. This research concluded that efficient vivianite formation can be achieved without a sludge digester, showing phosphorus recovery potential from undigested sludge via vivianite recovery. Besides, the recovery of vivianite from undigested sludge presents advantages like the reduction of the sludge to dispose of and mitigation of the vivianite scaling formation.
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